1. Field of the Invention
The present invention relates to a multilayer substrate made of thermoplastic resin, a component mounted board, and a method for producing a component mounted board.
2. Description of the Related Art
Among past inventions relating to multilayer substrates, for example, a semiconductor mounting method disclosed in Japanese Patent Application Publication No. 2006-120683 is known. In the semiconductor mounting method, bumps of a semiconductor bare chip are bonded to wires of a flexible wiring board, which includes films of liquid crystal polymer, by ultrasonic flip-chip bonding. By applying ultrasonic vibration to the semiconductor chip in a direction that is substantially the same as the alignment direction of the liquid crystal polymer, the wires and the bumps are bonded together.
The present inventors discovered that there is a possibility that the semiconductor bare chip will tilt during the bonding of the semiconductor bare chip to the flexible wiring board in the semiconductor mounting method disclosed in Japanese Patent Application Publication No. 2006-120683. Then, the present inventors considered the cause of the tilt of the semiconductor bare chip as follows.
The semiconductor bare chip may include a dense region where bumps are distributed densely and a sparse region where bumps are distributed sparsely. In this case, the flexible wiring board includes a dense region where wires which the bumps are to be bonded to are distributed densely and a sparse region where the wires are distributed sparsely. Accordingly, during the bonding of the semiconductor bare chip to the flexible wiring board, a relatively large number of bumps and wires contact each other in the dense regions, and a relatively small number of bumps and wires contact each other in the sparse regions.
When ultrasonic vibration is applied to the semiconductor bare chip, the semiconductor bare chip is pressed against the flexible wiring board by a mounting apparatus. Then, force is applied from the semiconductor bare chip to the flexible wiring board. A relatively large number of bumps and wires contact each other in the dense regions, and a relatively small number of bumps and wires contact each other in the sparse regions. Therefore, the force applied to the dense regions is greater than the force applied to the sparse regions. Accordingly, the wires in the dense regions sink deeper than the wires in the sparse regions, thereby causing a tilt of the semiconductor bare chip. When the mounting apparatus presses the top surface of the tilted semiconductor bare chip and applies ultrasonic vibration to the semiconductor bare chip, the force is concentrated on a part of the top surface of the semiconductor bare chip. This may cause a breakage of the semiconductor bare chip.